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* Fixed a bug that would cause allocate_page_run() to be called with an out of 

bounds index - the system would overwrite memory then and eventually KDL.
  This could best be reproduced with overlays after a while.
* Added a TODO comment that explains why free_cached_pages() might fail even
  though the page is actually free now.
* Added an explanation of how the sFreePageQueuesLock is to be used, thanks to
  Ingo for explaining it to me in the first place :-)


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@38895 a95241bf-73f2-0310-859d-f6bbb57e9c96
This commit is contained in:
Axel Dörfler 2010-10-08 07:40:42 +00:00
parent e0f9a0eac6
commit c5e2c3ec4d
1 changed files with 13 additions and 5 deletions
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18
src/system/kernel/vm/vm_page.cpp
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@ -1,6 +1,6 @@
/*
* Copyright 2010, Ingo Weinhold, ingo_weinhold@gmx.de.
* Copyright 2002-2009, Axel Dörfler, axeld@pinc-software.de.
* Copyright 2002-2010, Axel Dörfler, axeld@pinc-software.de.
* Distributed under the terms of the MIT License.
*
* Copyright 2001-2002, Travis Geiselbrecht. All rights reserved.
@ -125,6 +125,10 @@ static vint32 sModifiedTemporaryPages;
static ConditionVariable sFreePageCondition;
static mutex sPageDeficitLock = MUTEX_INITIALIZER("page deficit");
// This lock must be used whenever the free or clear page queues are changed.
// If you need to work on both queues at the same time, you need to hold a write
// lock, otherwise, a read lock suffices (each queue still has a spinlock to
// guard against concurrent changes).
static rw_lock sFreePageQueuesLock
= RW_LOCK_INITIALIZER("free/clear page queues");
@ -3189,15 +3193,14 @@ allocate_page_run_cleanup(VMPageQueue::PageList& freePages,
DEBUG_PAGE_ACCESS_END(page);
sClearPageQueue.PrependUnlocked(page);
}
}
/*! Tries to allocate the a contiguous run of \a length pages starting at
index \a start.
The must have write-locked the free/clear page queues. The function will
unlock regardless of whether it succeeds or fails.
The caller must have write-locked the free/clear page queues. The function
will unlock regardless of whether it succeeds or fails.
If the function fails, it cleans up after itself, i.e. it will free all
pages it managed to allocate.
@ -3220,6 +3223,7 @@ allocate_page_run(page_num_t start, page_num_t length, uint32 flags,
uint32 pageState = flags & VM_PAGE_ALLOC_STATE;
ASSERT(pageState != PAGE_STATE_FREE);
ASSERT(pageState != PAGE_STATE_CLEAR);
ASSERT(start + length <= sNumPages);
TA(AllocatePageRun(length));
@ -3298,8 +3302,11 @@ allocate_page_run(page_num_t start, page_num_t length, uint32 flags,
// free the page, if it is still cached
vm_page& page = sPages[nextIndex];
if (!free_cached_page(&page, false))
if (!free_cached_page(&page, false)) {
// TODO: if the page turns out to have been freed already,
// there would be no need to fail
break;
}
page.SetState(flags & VM_PAGE_ALLOC_STATE);
page.busy = (flags & VM_PAGE_ALLOC_BUSY) != 0;
@ -3382,6 +3389,7 @@ vm_page_allocate_page_run(uint32 flags, page_num_t length,
end = std::max(restrictions->high_address / B_PAGE_SIZE,
sPhysicalPageOffset)
- sPhysicalPageOffset;
end = std::min(end, sNumPages);
} else
end = sNumPages;